“The rapid pace with which Russia is seeking to modernize her military forces and weapons combined with the increasingly aggressive stance of the Russian military including Russian aircraft around the sovereign airspace of NATO states are all significant causes of concern”- he said in London.

"We are in familiar territory for anyone over the age of about 50 with Russia's aggressive behaviour a stark reminder it has the potential to pose the single greatest threat to our security," Hammond said.

"Hence continuing to gather intelligence on Russia capabilities and intentions will remain a vital part of our intelligence effort for the foreseeable future. It is no coincidence that all of our agencies are recruiting Russian speakers again.

Britain has been a vocal critic of Crimea's unification with Russia and its actions in eastern Ukraine and has pushed hard for Western nations to impose sanctions on Moscow."